1. Field of the Invention
The present invention relates to an acceleration switch and an electronic device.
2. Description of the Related Art
As a conventional acceleration switch, there is used an omnidirectional acceleration switch as described in Japanese Patent Application Laid-open No. Hei 09-145740, in which a counter electrode (central body) is provided inside a mass body and the mass body is supported by a beam. Such an acceleration switch is described below with reference to FIG. 1.
FIG. 1 is a cross-sectional view of the conventional acceleration switch. This acceleration switch 001 includes a peripheral portion (frame) 101, a beam 102, a mass body (weight) 103, and a counter electrode 104. One end of the beam 102 is fixed to the mass body 103 and the other end of the beam 102 is fixed to the peripheral portion 101. In this manner, the peripheral portion 101 supports the mass body 103 with the use of the beam 102.
In accordance with acceleration applied to the acceleration switch 001, the mass body 103 and the counter electrode 104 disposed inside the mass body 103 are brought into contact with each other. In this manner, an external device connected to the acceleration switch 001 detects vibration. In other words, when acceleration is applied to the acceleration switch 001, the mass body 103 moves to contact with the counter electrode 104, and the acceleration switch is turned ON. This acceleration switch has various advantages such as being available as a normally-off and omnidirectional switch and being relatively compact and mass-producible because monocrystalline silicon can be used as a base for production with the use of semiconductor manufacturing technology.
An acceleration switch to be mounted on an electronic device is highly required to be more compact, and hence a smaller external dimension of the acceleration switch is more advantageous. Cost of the acceleration switch is also highly required to be lower, and it is therefore further advantageous to use the semiconductor manufacturing technology to reduce the external dimension of the acceleration switch and thereby produce a large number of acceleration switches on a single wafer.
However, this is effective when the acceleration switch is placed horizontally, but the omnidirectional sensitivity is not effective depending on the usage of the acceleration switch, and a predetermined sensitivity may not be obtained.
For example, it is supposed that the acceleration switch is held perpendicularly (in the vertical direction) with respect to a horizontal plane (including a plane perpendicular to the vertical direction, a substantially horizontal plane, and a plane equivalent thereto). In the case where the acceleration switch is produced to have a sensitivity of, for example, 1 G or less, the switch becomes the ON state in response to the gravity of 1 G. FIG. 2A illustrates the case where the acceleration switch is held in parallel to the horizontal plane. FIG. 2B illustrates the case where the acceleration switch is held perpendicularly to the horizontal plane. In FIG. 2A, the horizontal plane is the XY plane, and the direction of gravity is the Z direction. In FIG. 2B, the horizontal plane is the XZ plane, and the direction of gravity is the Y direction (to be exact, the −Y direction). In the case where the acceleration switch is produced to have a sensitivity of 1 G or less, such as 1 G, when the switch is turned upright, the switch becomes the ON state because the gravity acceleration of 1 G has already been applied.
A specific description is now given. In the following, for simplification, a mass body and a counter electrode corresponding to the mass body 103 and the counter electrode 104 are only illustrated. In FIGS. 2A and 2B, the line AA′ represents a center line of a counter electrode 202 in the X direction (second direction), the line BB′ represents a center line of a mass body 201 in the X direction, and the line CC′ represents center lines of the counter electrode 202 and the mass body 201 in the Y direction (first direction) orthogonal to the thickness direction of a first substrate to be described later. The direction of gravity (vertical direction) in FIG. 2A is the Z direction, and the direction of gravity in FIG. 2B is the Y direction. Note that, in FIG. 2A, the line AA′ and the line BB′ are aligned with each other.
FIGS. 2A and 2B illustrate the case of an acceleration switch 002 having a sensitivity of, for example, 1 G. FIG. 2A illustrates the case where the acceleration switch 002 is placed horizontally. A distance “a” as an electrode interval between the counter electrode 202 and the mass body 201 is equal to a distance by which the mass body 201 displaces when an acceleration of 1 G is applied to the acceleration switch 002. Note that, a gap between the counter electrode 202 and the mass body 201 is uniformly the same as the distance “a” on the whole circumference. In this case, when the acceleration switch 002 is turned upright with respect to the horizontal plane, the mass body 201 displaces in the direction of gravity (vertical direction) in response to the gravity of 1 G.
As illustrated in FIG. 2B, the counter electrode 202 is brought into contact with a side wall of a through hole (hole portion) 205 on the C side, with the Y direction being the direction of gravity (vertical direction). The displacement amount in response to 1 G is equal to the distance “a” between the electrode of the mass body 201 and the counter electrode 202, and hence the mass body 201 is brought into contact with the counter electrode 202. In other words, the conventional technology has a problem in that a predetermined acceleration cannot be detected when acceleration other than an acceleration intended to be detected, such as the gravity acceleration, is applied. Note that, the electrodes to be electrically conductive by this contact are formed on opposing side walls of the mass body 201 and the counter electrode 202.